Traditional wood lattice, such as shown in FIGS. 2 and 3, has been long known and used for both decorative and functional purposes, as part of fences, porches, trellises, and other places. Traditional wood lattice consists of a first plurality of individual mutually parallel wooden slats 10 lying in a common plane and a second plurality of individual, mutually parallel wooden slats 12 lying in a second plane. The second plurality of slats 12 runs at an angle to the first plurality of slats 10 and is superposed on the first set of slats 10 to create a mesh-like appearance.
Traditional wood lattice has several drawbacks. First, because the lattice is typically used outdoors and the wood slats are exposed to the elements, the lattice requires periodic maintenance or its appearance will become unacceptable. Secondly, traditional wood lattice is expensive due to the cost of the wood slats and the cost of assembling the slats into a lattice. Another drawback to traditional wood lattice is that a sheet of lattice has a thickness equal to approximately twice the thickness of a single wood slat. For some applications, it is desirable to keep the thickness of the lattice down below a certain size. Traditional wood lattice may be made thinner by making each of the individual slats thinner. However, this reduces the overall strength of the lattice.
There have been numerous attempts to overcome the shortcomings of traditional wood lattice. For example, U.S. Pat. No. 2,672,658 to Pederson shows a wood lattice wherein specific combinations of tongues and grooves are formed such that the first and second sets of slats lie generally in the same plane. This creates a generally two-dimensional wooden lattice with a thickness less than would be created if the first and second sets of slats were superposed upon one another. However, the Pederson invention is expensive and time consuming to create and does not address the maintenance problems associated with wooden lattice. Also, many users prefer that lattice have a three-dimensional appearance. The Pederson invention attempts to create a three-dimensional appearance by the positioning of the wood grain of the various portions of the lattice. However, this is only partially successful as the wood grain will not always be apparent, especially if the lattice is painted.
Another alternative to traditional wood lattice is plastic lattice. Early plastic lattice was created by duplicating the construction of wood lattice. That is, sets of plastic slats, similar in dimension to wood slats, were molded and attached to one another with one set superposed on another set in the same way that wood lattice is formed. This design overcomes the maintenance limitations of traditional wood lattice but fails to address the thickness issue. Also, the cost of molding individual slats and assembling them into sheets of lattice is needlessly expensive. This approach fails to take advantage of one of the major advantages of plastic. That is, plastic molding often allows multiple piece assemblies to be molded as a single body.
Another approach to plastic lattice was two-dimensional plastic lattice, In this design, the first and second sets of slats laid in the same plane. This design allowed the plastic lattice to be molded as a one-piece body thereby giving significant cost advantages over the multi-piece plastic lattice. However, the two-dimensional plastic lattice failed to give the desired three-dimensional appearance of traditional wood lattice and multiple piece plastic lattice.
It is most efficient and cost effective if plastic injection molded parts have a generally uniform thickness throughout so that liquid plastic can flow from one part of the mold to another so that various parts of the injection molded piece cool at similar rates. Therefore, it would be difficult to injection mold a one-piece plastic lattice that exactly duplicated traditional wood lattice, because the areas where the first and second sets of slats overlap would be twice as thick as the portions where they did not overlap. This would lead to uneven cooling and difficulties with the flow of the liquid plastic.
U.S. Design Patent No. D402,381 to Gnida shows a molded plastic lattice that attempts to create a three-dimensional appearance similar to traditional wood lattice. This plastic lattice is shown in FIGS. 4 and 5. The plastic lattice disclosed in the Gruda patent attempts to give a three-dimensional appearance without having areas that are twice as thick as others. To accomplish this, the first and second sets of plastic slats intersect and overlap so that a majority of both the first and second sets of slats are in the same plane. However, one set of slats is offset from the second set of slats so that it sits above the other set of slats. This creates a three-dimensional appearance even though the first and second sets of slats are not offset as much as traditional wooden slats. However, the overlapping junction areas are only somewhat thicker than the rest of the slats. One drawback to this design is that the thicker junction areas use additional plastic and cool slower when compared to two-dimensional plastic lattice, as discussed previously. Another drawback is that the offsets may hinder the flow of liquid plastic in the mold. Also, the approach disclosed in the Gruda patent creates a lattice that is thicker than two-dimensional plastic lattice.